Solid rocket motors containing high burning rate ammonium perchlorate based composite solid propellants are required to be monitored to ascertain whether changes after manufacture result in the burning rate of the propellant, sensitivity, or other measureable changes to be out of system specification. The handling, transfer, and the required demilitarization, when the propellant does not meet the usefulness for which it was intended, can be extremely hazardous.
The following discussions relate to high burning rate ammonium perchlorate based composite solid propellants, particularly those propellants which use the ferrocene or the more expensive ferrocene derivative, liquid Catocene, the registered trademark for Syntex Chemicals, Inc. 2,2-bis(ethylferrocenyl)propane (C.sub.27 H.sub.32 Fe.sub.2). Of particular concern prior to the conception and reduction of practice of the invention disclosed hereinbelow is the lack of a suitable method to perform demilitarizations on rocket motors which have been determined to be out of system specification. Thus, demilitarization refers to the removing and destroying of the obsolete propellant since no satisfactory recovery method for the expensive propellant ingredients is available.
High burning rate ammonium perchlorate based composite solid propellants, such as in the Nike Zeus, utilize finely powered ferrocene (or dicyclopentadienyl iron) to achieve the desired burn rate augmentation. One of the main disadvantages of utilizing ferrocene in these propellants is its tendency to increase propellant sensitivities toward impact, friction, electrostatic and thermal degradation. Even though ferrocene possesses a melting point in the 174.degree.-176.degree. C. temperature range, it has a high vapor pressure and behaves like a volatile material. Because of this, it has a strong tendency to sublime during temperature cycling and recrystallize on the surface of the propellant grain. Continuing deposition of ferrocene on the grain surface will ultimately cause the burning rate of the propellant to be out of system specification. Additional concern comes from the realization that increased concentrations of ferrocene at the propellant surface can result in significant increases in propellant sensitivities. For example, a low percentage of ferrocene in the bulk propellant (e.g., 1-2%) may result in a much greater percentage ultimately recrystallized on the exposed propellant grain. If conditions are not monitored closely, this process can make the handling, transfer, and required demilitarization extremely hazardous. When such hazardous situations occur, demilitarization is accomplished by controlled burning and destruction of the motor. Alternatively, the propellant grain can be removed by using a water jet apparatus to cut and destroy the propellant. Neither of these methods allow for recovery and reclamation of any of the propellant ingredients.
Other high burn rate ammonium perchlorate based composite propellants often rely on the use of iron-containing burn rate catalysts, including ferrocenyl derivatives, as a catalyst ingredient to achieve the desired burn rate augmentation. Liquid Catocene is an example of such an ingredient that has received considerable attention and use by the propellant industry over the years. In addition to being an effective burn rate catalyst, Catocene also serves as a plasticizer in these propellants since it remains a liquid over the temperature storage and cycling regimes required of these missile systems. Its dual function gives Catocene a decided advantage over solid burn rate catalysts, such as ferrocene and iron oxide. Catocene's plasticizing abilities permit high oxidizer loadings to be achieved than would otherwise be possible. However, the major disadvantage of Catocene is its tendency to increase propellant sensitivities toward impact, friction, electrostatic discharge and thermal degradation. Several instances of accidental fires, injuries, and deaths have occurred with Catocene containing propellants. Catocene has been identified as the ingredient primarily responsible for increasing the hazards associated with these propellants. It is also an expensive ingredient costing $250 to $600 per pound depending on supplier and quantity. The recovery of Catocene during the demilitarization process would be beneficial. Because of the nature of Catocene and ferrocene-containing propellants and lack of suitable chemical recovery technology, demilitarization is usually accomplished by controlled burning and destruction of the motor hardware. Alternatively, the propellant grain containing ferrocene or a ferrocene derivative can be removed from the motor by using a water jet apparatus to cut and destroy the propellant. Likewise, as previously stated, neither of these two methods allow for the safe recovery and reclamation of the rocket motor hardware or any of the propellant ingredients, particularly, the recovery of waste chemicals in accordance with present and projected Environmental Protection Agency requirements.
The desirability of a method for demilitarization of high burning rate ammonium perchlorate based composite solid propellants, which efficiently recovers ingredients such as ferrocene and its derivatives, is well recognized by artisans in the solid propellant field.
Therefore an object of this invention is to provide a method for recovering ferrocene and its derivatives from solid propellant compositions.